An infant has persistent hyperphenylalaninemia despite a phenylalanine-restricted diet, along with truncal hypotonia, dystonia, and seizures. Tetrahydrobiopterin loading fails to normalize phenylalanine. Dihydropteridine reductase activity in fibroblasts is absent. Besides dietary phenylalanine restriction, therapy must include:

• A L-dopa, 5-hydroxytryptophan, and folinic acid ✓
• B Pyridoxine and betaine
• C Nitisinone and dietary tyrosine restriction
• D Sodium benzoate and sodium phenylbutyrate

Explanation

BH4 is the cofactor for tyrosine hydroxylase and tryptophan hydroxylase as well as phenylalanine hydroxylase. In DHPR deficiency, catecholamine and serotonin synthesis fail even after phenylalanine control, so L-dopa/carbidopa and 5-hydroxytryptophan are given, with folinic acid to counter cerebral folate depletion. Pyridoxine with betaine treats homocystinuria, nitisinone treats tyrosinemia I, and benzoate with phenylbutyrate scavenges ammonia in urea cycle defects.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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